A variety of techniques have been studied to remove particulate matters (PM) in exhaust gas discharged from an internal combustion engine. In Patent Document 1, a technique is proposed in which particulate matters are captured by a ceramic honeycomb filter, and when the amount of the captured particulate matters exceeds the predetermined acceptable value, the captured particulate matters are heated to be combusted away. In Patent Document 2, in order to overcome the drawback that the ceramic honeycomb filter used in Patent Document 1 is expensive, fragile and hard to handle, and in order to decrease the power consumption required for burning away particulate matters, a technique is proposed in which a combustion heater is placed between a permeable filter made of ceramic fiber and a heat insulator, and heating is performed by using the heater to burn particulate matters with a timing controlling the inflow of particulate matter-containing gas.
Since the techniques in the above Patent Documents 1 and 2 are a technique in which particulate matters are captured by a heat resistant filter and the captured particulate matters are heated to be combusted away in an arbitrary timing, there is concern about a reduced filter life due to a rapid temperature change, a local heating or the like. To address such issues, in Patent Document 3, a technique is proposed in which cracking means for cracking without causing a rapid temperature change or a local heating on a filter which captures particulate matters, and oxidizing means for oxidizing the residual combustion particulate matters by ozone gas are combined.
In Patent Document 4, a technique is proposed in which manganese oxide-supported substrate in a gas flow channel is placed and adsorbed particulate matters are oxidatively decomposed, as well as the oxidation decomposition of particulate matters is accelerated by further containing active species such as an OH radical, an oxide atom, oxygen ion and ozone gas. In this technique, particulate matters are charged by electrons generated at the time of discharge in a plasma discharge device so that the adhesion to manganese oxide-supported substrate is accelerated, and the oxidative decomposition of the particulate matters by the catalysis of manganese oxide can be effectively performed, and further, since an OH radical and ozone generated in the plasma discharge device per se oxidatively decompose the particulate matters, the particulate matters can be removed by oxidation.